In non-destructive testing using EMAT's, it is preferable for the stressed region to be struck by the incident wave at an angle of 90 degrees. This requires the EMAT to be oriented, data collected, then re-oriented for the next series of measurements. This practice involves large amounts of time in manually orienting and re-orienting the EMAT. The prior art does not allow for the rapid collection and analysis of data for calculation of stress in a specimen.
Further, the prior art involved measurement of signals on a specimen at a particular point in time. The measurements reflected certain characteristics of the specimen at the time the measurements were taken. Characteristics detected primarily included defects and flaws. Real time detection of the stress state of a specimen was not available.
Representative of the art is:
U.S. Pat. No. 5,813,280 (1998) to Johnson et al. discloses a force sensor including a cylindrical body having a central section and two distal sections wherein selected acoustic resonant modes are trapped in the central section and decays exponentially in the distal sections possibly using an electromechanical acoustic transducer (EMAT) to excite and detect the selected resonant modes in the central section.
U.S. Pat. No. 5,808,201 (1998) to Hugentobler discloses an improved electromagnetic acoustic transducer (EMAT) for monitoring uniaxially applied stress in an underlying workpiece.
U.S. Pat. No. 5,750,900 (1998) to Hugentobler et al. discloses an improved strain gauge and a method of using an electromagnetic acoustic transducer (EMAT) for monitoring stress and strain in an underlying workpiece.
U.S. Pat. No. 5,652,389 (1997) to Schapes et al. discloses a method and apparatus for the non-contact inspection of workpieces having a plate-like portion of the first part joined via an inertia weld to the end of a second part extending away from the plate-like portion.
U.S. Pat. No. 5,299,458 (1994) to Clark, Jr. et al. discloses an indication of the formability of metallic sheet which is determined using a correlation between nondestructively measurable ultrasonic properties and a formability index.
U.S. Pat. No. 5,115,681 (1992) to Bouheraoua et al. discloses a two-step method of studying the acoustic response of a piece by recording signals with acoustic sensors.
U.S. Pat. No. 5,811,682 (1998) to Ohtani et al. discloses an electromagnetic acoustic transducer for magnets and a sheet type coil unit.
U.S. Pat. No. 5,804,727 (1998) to Lu et al. discloses a method for determining and evaluating physical characteristics of a material.
U.S. Pat. No. 5,714,688 (1998) to Buttram et al. discloses a method of examining a ductile iron casting to determine a percent of nodularity present in the casting using an electromagnetic acoustic transducer (EMAT) system to determine a time-of-flight of an ultrasonic shear wave pulse transmitted through the casting at a selected location from which a velocity of sound in the casting can be determined.
U.S. Pat. No. 5,675,087 (1997) to MacLauchlan et al. discloses a device for measuring a load on a part and for monitoring the integrity of the part such as a bolt, comprises a socket having walls defining an interior space wherein the socket engages the bolt for transmitting a load to the bolt.
U.S. Pat. No. 5,619,423 (1997) to Scrantz discloses an improved system, method, and apparatus for the external ultrasonic inspection of fluidized tubulars and tanks.
U.S. Pat. No. 5,608,691 (1997) to MacLauchlan et al. discloses a shield for an electromagnetic acoustic transducer (EMAT) has multiple layers of electrically insulating and electrically conductive materials which contain a coil of the EMAT.
U.S. Pat. No. 5,537,876 (1996) to Davidson et al. discloses an apparatus and method for nondestructive evaluation for detection of flaws in butt welds in steel sheets using horizontal shear ultrasonic waves generated on the surface thereof.
U.S. Pat. No. 5,467,655 (1995) to Hyoguchi et al. discloses a method and apparatus for measuring properties of a cold-rolled thin steel sheet, comprising an electromagnetic ultrasonic wave device, a computing device, and a controlling device for executing the measurement of properties and the computation.
U.S. Pat. No. 5,237,874 (1993) to Latimer et al. discloses a method and apparatus of non-destructive testing wherein a generally bi-directional wave-generating electromagnetic acoustic transducer is pivotally mounted upon a base with this transducer being continuously rotated or oscillated upon the base as it is moved with respect to the workpiece (or the workpiece is moved with respect to the base).
U.S. Pat. No. 5,164,921 (1992) to Graff et al. discloses an electrodynamic permanent magnet transducer for the non-destructive testing of workpieces by means of ultrasound.
U.S. Pat. No. 5,050,703 (1991) to Graff et al. discloses an electrodynamic transducer head for a non-destructive testing of workpieces with electrically conductive surfaces by way of ultrasound.
U.S. Pat. No. 4,522,071 (1985) to Thompson discloses a method and apparatus for determining stress in a material independent of micro-structural variation and anisotropy's.
U.S. Pat. No. 4,466,287 (1984) to Repplinger et al. discloses a method for non-contact, non-destructive testing of a test body of ferromagnetic and/or electrically-conductive material with ultrasound waves.
U.S. Pat. No. 4,295,214 (1981) to Thompson discloses an electromagnetic acoustic transducer, including an electrical conductor adapted to carry an alternating current in a current plane.
What is needed is a rotating EMAT, connected to a processor, that can be rotated through 360 degrees. What is needed is a rotating EMAT connected to a processor using an algorithm to calculate birefringence from the normalized differences in the phase of SH waves in a specimen. What is needed is a rotating EMAT connected to a processor using an algorithm to calculate the pure-mode polarization directions of SH waves in a specimen. What is needed is a rotating EMAT connected to a processor using an algorithm to calculate the stress in a specimen. What is needed is a rotating EMAT connected to a processor used as a strain gage.